1. Field of the Invention
This invention relates to a link coupling device for use in a link mechanism oscillating two or more wiper blades through a single wiper motor in an electric wind-shield wiper assembly which wipes off raindrops and the like from, for example, a front windowglass of an automobile.
2. Related Art Statement
As the conventional link coupling device, there is for example, a device as shown in FIG. 3 and described in Japanese Utility Model laid open No. 58-122646.
This conventional device comprises a ball pin 110 fixed to a motor link arm 120, and a ball retainer 101 attached to a link connecting rod 118 and receiving the ball pin 110 therein. The ball pin 110 is made of a metal and comprises a spherical portion 111 and a cylindrical fixing portion 112 fixed at its end to the motor link arm 120. In the upper part of the spherical portion 111 is formed a circular 113.
On the other hand, the ball retainer 101 is made of a synthetic resin and has an approximately spherical shell shape having an opening 105 and provided inside the opening with a force-fitting portion 102 capable of press-fitting the spherical portion 111 of the ball pin 110 into the inside thereof. Furthermore, the ball retainer 101 is provided at the outer periphery with a collar portion 104 in parallel with the opening 105. A receiving groove 104a is formed in the collar portion 104, which receives the link connecting rod 118 through a receiving hole 118a formed therein to thereby attach the ball retainer 101 to the link connecting rod 118. Moreover, a protrusion 103 capable of freely inserting into the dent 113 of the ball pin 110 is arranged in the force-fitting portion 102 of the ball retainer 101 at the inner part thereof. When the ball retainer 101 is force-fitted to the spherical portion 111 of the ball pin 110, the protrusion 103 of the ball retainer 101 becomes inserted into the dent 113 of the ball pin 110, and consequently the unnecessary distortion of the ball retainer 101 is controlled by contacting the peripheral wall 103a of the protrusion 103 of the ball retainer 101 with the side wall 113a of the dent 113.
However, when the unnecessary distortion movement of the ball retainer 101 force-fitted into the ball pin 110 is controlled by contacting the peripheral wall 103a of the protrusion 103 in the ball retainer 101 with the side wall 113a of the dent 113 in the spherical portion 111 of the ball pin 110, since a protruding portion subjected to a larger force is formed as the protrusion 103 of the ball retainer 101 made of the synthetic resin, cracks may be produced in the base of the protrusion 103 to cause fracture, and consequently the loss of the link function is brought about by the contact between the link connecting rod 118 and the motor link arm 120 due to the excessive movement of the ball retainer 101 and the like.